In the extraction of oil from fruit such as nuts, seeds, and the like it is necessary to comminute the fruits completely, thereby destroying the cell wall which retained the oil. This is done in a two-stage process: first the fruits are crushed, then the crushed fruits are heated. These two steps are always carried out regardless of the stage at which the oil is extracted. Sometimes the oil is extracted at the crushing press, and sometimes it is extracted from the heated crushed pulp by means of a solvent.
As a general rule the first step, that is comminuting or crushing the oil fruit, is carried out by means of crushing rollers. These rollers are ridged and the oil fruits are passed through them several times, or are passed through several pairs of such rollers. Finally, the crushed fruits are passed between a pair of smooth rollers which squeeze the mass of granulates together. The rolls generally are set at a gap of 0.2 mm in order to ensure that the cell walls of the fruits are completely destroyed. This close spacing has the considerable disadvantage that should any sand or other abrasive particles find their way into the process, the rollers become worn. In practice rollers rapidly wear out at their central regions so that after only a relatively short service life they must be removed and turned down.
The thermal treatment generally takes place in large pans which are loaded into an oven in levels from 400 to 700 mm apart. It is common practice to provide agitating or mixing elements which ensure that the entire crushed mass is properly roasted. Such a roasting process is relatively lengthy as the crushed mass itself is a good insulator and requires a very long time to heat up fully. Should the extraction process break down somewhere along the way it is necessary to finish roasting the batch in process before the oven too can be shut down. Another difficulty with these ovens is that they are generally of gas type, requiring air circulation over the mass being heated so that much of the oil is lost in the form of vapor while the time necessary to heat the crushed nuts and seeds is again increased.
The principal difficulty with the hitherto known system is that it requires a great detail of expensive equipment which takes up much floor space. The process is not very efficient and is relatively costly in terms of the energy required to produce a given quantity of oil. Of course with the proliferation of different pieces of equipment the possibility of breakdown and the severity of the consequences thereof increases.